258 HISTORY OF FORMAL ASTRONOMY. 



centric Theory (that which places the centre of the celestial motions it 

 the Sun) had a claim to assent so decidedly superior to the Geocentric 

 Theory, which places the Earth in the centre ? What is the basis oi 

 the heliocentric theory? That the relative motions are the same, on 

 that and on the other supposition. So far, therefore, the two hypoth- 

 eses are exactly on the same footing. But, it is urged, on the helio- 

 centric side we have the advantage of simplicity : true ; but we have, 

 ' on the other side, the testimony of our senses ; that is, the geocentric 

 doctrine (which asserts that the Earth rests and the heavenly bodies 

 move) is the obvious and spontaneous interpretation of the appear- 

 ances. Both these arguments, simplicity on the one side, and obvious- 

 ness on the other, are vague, and we may venture to say, both inde- 

 cisive. We cannot establish any strong preponderance of probability 

 in favor of the former doctrine, without going much further into the 

 arguments of the question. 



Nor, when we speak of the superior simplicity of the Copernican 

 theory, must we forget, that though this theory has undoubtedly, in 

 this respect, a great advantage over the Ptolemaic, yet that the Coper- 

 nican system itself is very complex, when it undertakes to account, as 

 the Ptolemaic did, for the Inequalities of the Motions of the sun, 

 moon, and planets ; and, that in the hands of Copernicus, it retained 

 a large share of the eccentrics and epicycles of its predecessor, and, in 

 some parts, with increased machinery. The heliocentric theory, with- 

 out these appendages, would not approach the Ptolemaic, in the accu- 

 rate explanation of facts ; and as those who had placed the sun in the 

 centre had never, till the time of Copernicus, shown how the inequal- 

 ities were to be explained on that supposition, we may assert that 

 after the promulgation of the theory of eccentrics and epicycles on the 

 geocentric hypothesis, there was no imllixhed heliocentric theory 

 which could bear a comparison with that hypothesis. 



It is true, that all the contrivances of epicycles, and the like, by 

 which the geocentric hypothesis was made to represent the phenomena, 

 were susceptible of an easy adaptation to a heliocentric method, when 

 a good mathematician had once 2^'oposed to himself the problem : and 

 this was precisely what Copernicus undertook and executed. But, till 

 the appearance of his work, the heliocentric system had never come 

 before the world except as a hasty and imperfect hypothesis ; which 

 bore a favorable comparison with the phenomena, so* long as their 

 general features only were known ; but which had been completely 

 thrown into the shade by the labor and intelligence bestowed 



